You would have to do a lot of towing to make a significant difference. Good idea, but cant see the cost benefit. I own an 01 HD for instance that gets 10 to 12 no matter what i tow. And still only gets 12 not towing anything. Unless your making a couple trips out west each year or long trips in general, i don't see the savings being worth the effort. You might gain a mile per gallon, maybe two if your lucky.